This invention relates to an attenuator and more particularly to an attenuator which can be remotely controlled in a stepwise manner to permit placement within a broadcast transmission system to thereby control the modulation level of the audio signal.
In a broadcast transmission system there is typically provided a modulation limiter circuit which is connected to the transmitter for sending out the audio signal. In order to control the modulation level, an attenuator is generally placed between the modulation limiter and the transmitter. Most of these attenuators require direct control at the broadcast station. However, more recently there has become a need for remote control systems for remotely setting the modulation level.
In order to provide such remotely controlled attenutation, there has been utilized devices such as a mechanical potentiometer or a rotary attenuator. A reversible motor is utilized to operate such devices. However, these systems have the disadvantage of including backlash, imperfect tracking between channels in a multichannel installation, poor impedance match and impedance variation, and other technical problems. Additionally, and perhaps of most importance, is that the operator is not able to control the attenuation in known, precise small increments. In utilizing such prior art remote control attenuators a raise or lower button is initiated and the attenuator is operated in a trial and error fashion until the desired attenuation is achieved.
Such systems of modulation control utilize a control button which continuously operates during the length of time that the button is energized. As long as the button is depressed, the modulation level continues to change. During the length of time that the control button is depressed, the oscillator continues to raise or lower the value and thereby continuously feed the variation to the system. However, here too the individual cannot accurately determine the modulation level that he desires since there is such continuous ongoing changes.
Accordingly, there is need for a remote control precision step attenuator which provides precise stepwise increments or decrements of the modulation level within small tolerance values. Such system should also provide excellent channel tracking while permitting multiple channels to operate. Impedance variation should be constant and backlash should be avoided.